1. Technical Field
The present inventive concept relates to a method of forming a contact and to a method of manufacturing a phase change memory device using the same.
2. Description of the Related Art
Non-volatile memory devices using a resistance material include phase change random access memories (PRAMs), resistive RAMs (RRAMs), magnetic RAMs (MRAMs) and the like. A dynamic RAM (DRAM) or flash memory device stores data using charges, whereas a non-volatile memory device using a resistance material stores data using a change of the state of a phase change material such as chalcogenide alloy (in the case of a PRAM), a change in resistance of a variable resistance material (in the case of an RRAM), a change in resistance of a magnetic tunnel junction (MTJ) thin film according to the magnetized state of a ferromagnetic material (in the case of an MRAM) or the like.
For example, in a phase change memory device, the state of the phase change material changes, from one of a crystalline state and an amorphous state to the other, as the phase change material cools after being heated. The phase change material in the crystalline state has a low resistance and the phase change material in the amorphous state has a high resistance. Accordingly, the crystalline state may define set data or “0” data, and the amorphous state may be define reset data or “1” data.
Phase change memory devices, like most semiconductor devices, are made up layers of patterns of circuit elements, which will be simply referred to hereafter as circuit patterns. A circuit pattern is conventionally formed using photolithography. In general, photolithography includes an exposure process in which a layer of photoresist on a target layer is exposed to an image corresponding to the desired circuit pattern, and a developing process in which the exposed or non-exposed portions of the layer of photoresist are removed, resulting in the formation of a photoresist pattern. Then the target layer is etched using the photoresist pattern as a mask.
Recently, the size and spacing of features constituting a circuit pattern are being gradually decreased to attain higher degrees of integration in phase change memory devices. In this respect, the resolution of the photolithography process imposes limits on the degree to which circuit patterns can be scaled down. Therefore, different techniques are being studied and developed in an attempt to increase the resolution of photolithography. For example, light sources that generate light of shorter wavelengths for use in the exposure process have been developed.